Chemical mechanical polishing machines for semiconductor wafers are known in the prior art and are typified by U.S. Pat. No. 5,593,344 and the patent referenced therein. Generally these machines are customized for a customer's particular requirements and facility area. Further, most if not all of the prior art machines perform the polishing step(s) while the semiconductor wafer is in a horizontal position i.e. the wafer is positioned horizontally on a rotating horizontal table or horizontal belt section and a downward force is exerted on the wafer top side. This is done usually by a first platen or wafer carrier moving down with the wafer(s) to force the wafers against a second slurry-containing polishing platen or belt.
Chemical mechanical polishing (CMP) in semiconductor processing removes the highest points from the surface of a wafer to polish the surface. CMP operations are performed on partially processed wafers. A typical wafer is crystalline silicon or another semiconductor material that is formed into a nearly circular wafer. A typical processed or partially processed wafer when ready for polishing has a top layer of a dielectric material such as glass, silicon dioxide, or silicon nitride or a metallic layer over one or more patterned layers that create local topological features on the order of about 4000-10,000 .ANG. in height on the wafer's surface. Polishing smoothes the local features so that ideally the surface of the wafer is flat or planarized over areas the size of a die to be formed from the wafer. Currently, polishing is sought that locally planarizes the wafer to a tolerance of about 1500-3000 .ANG. over the area of a die.
A conventional belt polisher includes a belt carrying polishing pads, a wafer carrier head on which a wafer is mounted horizontally, and a support assembly that supports a horizontal portion of the belt under the wafer, as seen in FIG. 1 of the U.S. Pat. No. 5,593,344 patent. For CMP, the polishing pads are coated or sprayed with a slurry, and a drive system rotates the belt. The carrier head brings the wafer into contact with the polishing pads so that the rotating polishing pads slide against the surface of the wafer. Chemical action of the slurry and the mechanical action of the polishing pads against the surface of the wafer remove material from the surface. The '344 patent and U.S. Pat. No. 5,558,568 describe CMP systems using hydrostatic fluid bearings to support a belt. To polish a surface to the tolerance required in semiconductor processing, CMP systems generally attempt to apply a polishing pad to a wafer with a pressure that is uniform across the wafer. Methods and structures that provide uniform polishing are sought.
Further, since the prior art machines are increasingly being automated with robotic wafer loading and unloading systems, it has become desirable to reduce the complexity of the robotic system and to minimize the elapsed time for each unit operation and thus increase the efficiency of both the robotic system and the polishing machine. A need has also arisen to provide a more standard polishing machine at less cost which is adapted to virtually any production rate need and to fit into a broad range of facility spaces.